This invention relates to a fluorescent display device of a triode structure including an anode, a cathode and a mesh grid, and more particularly to a fluorescent display device of the dot matrix type wherein a plurality of anode segments are arranged in a matrix-like manner at fine pitches.
A conventional fluorescent display device of this type is disclosed in Japanese Patent Publication No. 202050/1982, which is generally constructed in such a manner as shown in FIG. 4. More specifically, the fluorescent display device includes a plurality of dot-like anode segments arranged in a matrix-like manner. Each of rows of the matrix is provided with three wiring conductors a, b and c and the anode segments A of each row are connected to the same wiring conductor at every third interval. Grids G each are arranged for every two columns of the matrix. At the time of driving of the fluorescent display device, each adjacent two grids are concurrently fed with a positive scan signal and circulatingly scanned while shifting the grids one by one in a predetermined direction. The grids G which are not fed with a display signal are fed with a negative scan signal. Then, of the anode segments A of four columns corresponding to the two grids G fed with the positive scan signal, the anode segments A of two columns on an inside or a side on which both grids G are adjacent to each other are fed with a display signal at a timing in synchronism with scanning of the grids G.
In general, a fluorescent display device has been improved so as to provide a display highly densified depending on applications thereof. The conventional graphic fluorescent display device described above is likewise subject to high densification of the anode segments, so that there is a tendency that pitches at which the anode segments are arranged are reduced. For example, when the anode segments are formed into a square of which one side is 0.45 mm and arranged at pitches of 0.65 mm, a distance between each adjacent two anode segments is caused to be only 0.2 mm. Thus, in the conventional graphic fluorescent display device, it is required to arrange side edges of each two mesh grids opposite to each other at an interval as small as 0.1 mm or less in such a reduced space between each adjacent two anode segments while preventing contact between the side edges of the mesh grids opposite to each other. Arrangement of the mesh grids with such high accuracy requires skill. In this instance, biased arrangement of the mesh grids between the anode segments causes some disadvantages.
More specifically, as shown in FIG. 5, when, of the anode segments A3 and A4 of two columns positioned inside two grids G2 and G3 which are fed with a positive scan signal, the anode segment A4 of one column is fed with a display signal, the next anode segment A1 but two is likewise fed with the display signal. A mesh grid G1 corresponding to the anode segment A1 is fed with a negative scan signal, to thereby normally prevent electrons from impinging on the anode segment A1. However, when an edge of the mesh grid G1 is biasedly arranged so as to be in proximity to an edge 100 of the anode segment A1, a positive electric field of the mesh grid G2 adjacent thereto causes electrons to fly into the edge 100 of the anode segment A1, leading to leakage luminance.